Dinosaurs Shared Earth with Older Animals, Study Shows

Dinosaurs, contrary to conventional wisdom, did not suddenly appear 220 million years ago and quickly dominate the world by out-competing and sending more archaic animals into extinction.

Instead, according to new evidence published in Friday's edition of the research journal Science, the first dinosaurs were relatively small creatures who had to share the world with those more archaic animals for 15 million to 20 million years.

Discovery of an archaic animal's fossil remains in the Petrified Forest of New Mexico's Ghost Ranch last year is causing paleontologists to rethink the path dinosaurs took to dominance.

The fossil is not that of a dinosaur but a very close cousin, given the name by its discoverers as Dromomeron romeri (dro-MO-mer-on RO-mer-eye). It belonged to an archaic group of animals called "basal dinosauromorphs" - pre-dinosaurs that until now were thought to have gone extinct when dinosaurs first appeared a little more than 220 million years ago.

What makes its discovery so remarkable is not the animal itself, but that the fossil bones of such a close pre-dinosaur relative have been found mixed in with fossil bones of true dinosaurs.

"This discovery is a very significant piece of work," said an admiring Nick Fraser, curator of vertebrate paleontology at the Virginia Museum of Natural History, an authority on pre-dinosaur life who was not part of the discovery team.

"I think it answers some questions paleontologists have been seeking for a long time. It tells us that the appearance of dinosaur life in the late Triassic period (208 million to 220 million years ago) was not, as we previously believed, a sudden, abrupt event."

The four principle scientists who designed and mounted the expedition that discovered Dromomeron are graduate students working toward their PhDs, including Nathan Smith, 27, a Crystal Lake native who is a University of Chicago PhD candidate and Field Museum research associate.

"These things aren't necessarily direct ancestors to dinosaurs," said Smith, who currently is studying some of the recovered Dromomeron bones at the Field.

"They are side branches of an ancestor. But finding them gives us a clearer idea of how the earliest dinosaurs evolved."

Dromomerons, said Smith, were relatively fragile creatures about 2 feet tall that ran on their two hind legs. The fossils recovered so far are incomplete and without an intact skull, so the discoverers don't yet know if they were meat eaters or herbivores.